1. Field of the Invention
The present invention relates to a process for plasma depositing silicon nitride or silicon dioxide films onto a substrate. In particular, the present invention relates to a process for plasma depositing silicon nitride or silicon dioxide films onto a substrate wherein di-tert-butylsilane is employed as a silicon source for these films.
2. Brief Description of the Prior Art
Chemical vapor deposition (CVD) is used throughout the microelectronics industry for semiconducting and insulating thin film deposition. When films such as silicon nitride (Si.sub.3 N.sub.4) or silicon dioxide (SiO.sub.2) are deposited, silane (SiH.sub.4) is generally used as the gaseous silicon source.
Silicon nitride and dioxide, important materials in the production of integrated circuits, are used as gate dielectrics, diffusion masks, and passivation films. Silicon nitride has a high dielectric strength, excellent barrier properties against impurity diffusion, and good chemical stability. Silicon dioxide has good insulating properties and is chemically stable for these applications.
Silane is highly toxic and spontaneously flammable in air. It requires the use of expensive gas cabinets and a cross purging gas supply system. Special purging procedures are needed before introduction into deposition equipment. A number of silicon containing chemicals have been used or proposed as silicon sources for nitride and oxide CVD. These include silicon tetrachloride (SiCl.sub.4), silicon tetrabromide (SiBr.sub.4), silicon tetrafluoride (SiF.sub.4), dichlorosilane (SiH.sub.2 Cl.sub.2), and disilane (Si.sub.2 H.sub.6). Other chemicals such as tetramethylorthosilicate [TMOS Si(OCH.sub.3).sub.4 ], tetraethylorthosilicate [TEOS, Si(OC.sub.2 H.sub.5).sub.4 ] and tetramethylcyclotetrasiloxane (TMCTS, C.sub.4 H.sub.16 Si.sub.4 O.sub.2) are used only for oxide deposition. All of the above halogen containing silanes are toxic and corrosive themselves in addition to producing toxic and corrosive by-products. Disilane is a flammable, toxic gas that requires similar handling procedures to silane. Presently, if a microelectronics manufacturer wants to limit its use of silane, TMOS, TMCTS and TEOS are the only commercially feasible alternatives for silicon dioxide deposition. There are no commercially feasible alternatives to silane for silicon nitride deposition.
Accordingly, there is a need for better alternatives to silane in these CVD processes. The present invention is a solution to that need.
Separately, di-tert-butylsilane (DTBS) is a known chemical with a Chemical Abstracts registry number [30736-07-3]. Processes for making DTBS are disclosed by Watanabe et al "A Simple and Convenient Method for Preparing Di-t-Butyl Silanes", Chemistry Letters pp. 1321-1322, 1981; Doyle et al "Hindered Organosilicon Compounds. Synthesis and Properties of Di-tert-butyl-, Di-tert-butylmethyl-, and Tri-tert-butylsilanes", J. Am. Chem. Soc., 97, pp. 3777-3782 (1975) and Triplett et al, "Synthesis and Reactivity of Some t-Butyl-Disilanes and Digermanes", Journal of Organometallic Chemistry, Vol. 107, pp. 23-32 (1976). All three of these articles are incorporated herein by reference in their entireties. DTBS has been used as a silylation agent to hydroxy compounds (CA 101: 91218v) and as an intermediate in the production of di-tert-butyldichlorosilane (CA 98: 126375t).
Di-tert-butylsilane is an air-stable, non-corrosive liquid. It is soluble in many organic solvents and does not react with water. Its high vapor pressure at room temperature allows for easy introduction into CVD reactors. No gas cabinets or cross purging systems are needed in order to use this chemical in CVD reactors. The decomposition by-products are not corrosive in nature. Thus, according to the present invention, di-tert-butylsilane represents a silicon source that may be used for both nitride and oxide deposition.